Iron-cored coil



June 30, 1942.

w. s. CHALLIS 2,288,120

IRON-CORE]? COIL Filed Nov. 18, 1959 INVENTOR WILL/AM S/OA/E) CHALL/S IBY ATTORNEY Patented June 30, 1942 IRON-CORED COIL William SidneyChallis,

Hayes, England, assignor to Electric & Musical Industries Limited,Hayes,

Middlesex, Britain England,

a company of Great Application November 18, 1939, Serial No. 305,108 InGreat Britain November 10, 1938 1 Claim.

tionate direct current to flow in a coil, the value of" said directcurrent determining the permeability of the iron core on which is wounda coil which is connected in the local oscillator circuit, the circuitbeing such that departure of the intermediate frequency from itsassigned value causes the constants of the coil which is connected inthe local oscillator circuit to alter in such a manner that theintermediate frequency produced approaches closer to its assigned value.

It has previously been proposed to vary the constants of a circuitconnected to a coil in which high frequency currents are adapted to flowby utilising the Variations in direct current adapted to flow throughanother coil, both the coils being wound on iron cores ferent materials,the coil in which high frequency currents are adapted to flow beingwound on a core formed from high frequency powder core material.

It has been found, contrary to what would normally be expected, that lowfrequency core material may satisfactorily be employed in connectionwith the coil adapted to carry high frequency current, and it is theobject of the present invention to make use of this fact.

According to one feature of the present invention there is provided acircuit including a coil arrangement comprising two coils arranged aboutan iron core of low frequency material wherein one of said coils isadapted to carry direct current and is connected to a direct currentcircuit and the other of said coils is adapted to carry high frequencycurrent and is connected to a high frequency circuit, the arrangementbeing such that when a change in the direct current occurs thepermeability of the core is changed so as to produce a change in theconstants of the high frequency circuit.

According to another feature of the present invention there is provideda coil arrangement comprising a coil adapted to carry direct current anda coil adapted to carry high frequency current said coils being disposedabout an iron core of low frequency material formed in two opposinggroups of laminated E-shaped stampformed of dif ings, the core forming aclosed path around said coils which are spaced apart and surround thecentre limbs of said core, the arrangement being such that a change incurrent in the coil adapted to carry direct current causes thepermeability of the core to change so as to enable a change to beproduced in the constants of a circuit associated with said coil adaptedto carry high frequency current.

In order that the present invention may be clearly understood andreadily carried into effect it will now be described with reference tothe accompanying drawing in which Fig. 1 illustrates a longitudinalsection along the line of Fig. 2, and Fig. 2 illustrates aplan of apresent preferred embodiment of the invention by way of example.

The iron-core consists of a series of laminated E-shaped stampingscomposed of the two series having reference numerals l and 2, thelaminated stampings of each series being face to face and both seriesbeing maintained adjacent one another with the limbs of one seriesoverlapping the limbs of the other series. The laminated stampings ofeach series may, if desired, be alternately interleaved but this methodof packing the stampings introduces air gaps at the nonoverlappingportions of the stampings. Surrounding the centre limbs and enclosed bythe outer limbs of the stampings there is a coil former or bobbin ofinsulating material comprising the two parts 3 and 4 made in one piece,the part 3 having wound therein a coil 5 adapted to carry directcurrent, while the coil 6 adapted to carry high frequency current isWound on the part 4 of the coil former, the coil 6 surrounding only thecentre limbs of the series of laminated stampings 2.

It will also be seen from Fig. 2 that the portion of the core materialassociated with the coil 5 has a larger area of cross section than theportion of the core material associated with the coil 6. Further,although the limbs of the stampings I may extend further towards andbeyond the coil 6 as compared with the position shown in theaccompanying drawing, the relative positions there shown, with the limbsof the stampings I not encroaching upon the space occupied by the coil6, are preferred.

The distance between the adjacent ends of the coils 5 and 6 should begreater than a minimum value, below which minimum value the arrangementis bound to be inefficient, and the maintenance of this minimum valuemay be assured by making the portion 1 of the coil former sufficientlywide. In one particular case in which the iron core is 1 in length, andhas approximately the same dimension for its overall width, the centrallimbs of the stampings being approximately A" wide, a convenient valuefor the spacing between the coils 5 and 6 is 1%" The number of turns onthe coils does not appear to be of primary importance in thisconnection, as the same value for the spacing between the coils 5 and 6is adopted in arrangements wherein the coil 5 has about 3000 turns, orabout 500 turns, and the coil 6 has up to about 40 turns.

The series of laminated stampings indicated at I and 2 of which the ironcore is composed is made of metal such as is usually used for the coresof low-frequency transformers in radio receivers, for example that knownunder the registered trade-mark Mu-metal, and'the coils may be tapped sothat different portions of the coils may be utilised in differentcircuits in any desired manner. The "central limbs'o'f the laminatedstampings 2 are made to lie as close as possible to thecentral-portionof the coil 6 by making the "portion of thecoil former '4 whichlies adjacent-the central portion of the stampings 2 as thin asconvenient. The 'tappings to the coils *5 and ii may be'brought outtoterminals aflixedto a piece of insulating material 8 which is shaped soas to be held in position by the stampings 2 and the outer portion ofthe part 4'0f the former. The wire used in the coil 6 may be-wirespecially suitable for-carrying high frequency currents,'such as litzwire.

'The series of laminated stampings I and 2 are maintained rigidlypositioned with respect to each other by-clips indicated at"9 made ofcopper,

fixed to the adjacent ends of the laminated stampings I and 2, and by awedge I0, made of insulating material, partially inserted into theinterior of the coil former 3 and thereby held rigidly against the innerlimbs of the laminated stampmgs.

It may be desirable to bias the core comprised of the series oflaminations I and -2 by giving it a definite permeability value, and forthis purpose'a biassing coil may be arranged on the iron core inaddition to the coils 5 and 6, and this biassing coil may, for example,be wound on the inner part of the former carrying the coil 5.

A coil arrangement according to the present invention may be utilised inany circuit wherein the change in permeability of an iron core due tovariations of current in one coil are required toinfiuence the constantsof a circuit associated with another coil, but has been primarilydesigned for use for the automatic frequency control of radio receivers.

In arrangements wherein the coil 5 is connected in a valve circuit, suchas the cathode or anode icircuit of a valve, the said coil will besupplied with a definite amount of current dependent upon the circuitconditions. If it is required to have a permeability bias in the ironcore of a required value, then such a permeability bias may be obtainedby providing the coil 5 with an appropriate number of turns. With thecoil 6 connected to the local oscillator circuit of a receiver, it isdesirable to obtain as great a change as possible in frequency of thelocal oscillator for a given change in current in the coil 5, and thismay be achieved by increasing the number of turns in the coil 5.However, if this increase in the number of turns alone were effected,the permeability bias of the core would be varied from the requiredvalue. In order to offset this change in the permeability bias of thecore the aforesaid biasing coil may be used or a further coil employed,either of these latter coils being given a suitable number of turns andsupplied with a suitable current so that the permeability of the ironcore is restored substantially to its required value, although theoriginal coil 5 has an increased number of turns. Such further coil maybe wound on the same former as the original coil 5, and may be suppliedwith direct current from a separate source or from the same source asthe high tension supply of the valve in the circuit of which theoriginal coil 5 is connected.

By this means of providing an. increased number of turns in the coil 5,and another coil to offset the permeability bias change in the iron corefrom its required value, an increased frequency change is obtained for agiven change in the current in the original coil 5, the permeabilitybias of the core being maintained substantially at the required value.

I claim:

In a variable high frequency inductance device, a direct current controlwinding, 2. high frequency inductance winding made of a wire suitablefor carrying high frequency currents, an iron core composed of lowfrequency material forming a closed magnetic path around said windingsaid iron core being made up of a pair of laminated E-shaped auxiliarycores mounted face-to-face adjacent one another and with theirrespective limbs partially overlapping, said control Winding being woundaround that portion of the central limb of said iron core which includesat least a part of the un-overlapped portion of the central limb of oneof said auxiliary cores and the overlapped portion thereof, said highfrequency winding being in axial alignment with said control winding,said high frequency winding being spaced from said control winding by adistance exceeding a predetermined minimum value and wound around onlythe'un-overlapped portion of the central limb of the other of saidauxiliary cores, a cylindrical coil support for said control windingconcentric with said central limb portion, said support being providedwith a spacer flange located between said two windings, said flangehaving a thickness to provide said minimum value spacing, "thearrangement being such that a change in current in the direct currentwinding causes the permeability of the core to change and therebyproduce a change in the inductance of the other winding, the portionofthe iron core associated with the direct current winding having agreater cross-section area than the portion of the iron core associatedwith the high frequency induct-

